<!DOCTYPE html>
<html lang="en">

<head>
    <meta charset="UTF-8">
    <meta http-equiv="X-UA-Compatible" content="IE=edge">
    <meta name="viewport" content="width=device-width, initial-scale=1.0">
    <title>Document</title>
    <style>
        body {
            font-size: 60px;

        }

        .box1,
        .box2,
        .box3 {
            width: 200px;
            height: 200px;
        }

        .box1 {
            background-color: #bfa;
            position: absolute;
            /* z-index:1 ; */
            /* 开启了定位元素，可以通过 z-index: 属性来指定元素的层级
             z-index: 需要一个整数作为参数，值越大层级越高
             元素的层级越高越优先显示
             元素的层级一样，优先显示靠下的元素
             祖先元素层级再高也不会盖住后代元素
             */
        }

        .box2 {
            position: absolute;
            background-color: rgba(255, 0, 150, 0.3);
            top: 50px;
            left: 50px;
        }

        .box3 {
            background-color: yellow;
            position: absolute;
            top: 100px;
            left: 100px;
        }
        .box4{
            width: 50px;
            height: 50px;
            position: relative;
            background-color: powderblue;


        }
    </style>
</head>

<body>
    <div class="box1">1</div>
    <div class="box2">2</div>
    <div class="box3">3
        <div class="box4">4</div>
    </div>
</body>

</html>